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Composite shear wall is a structural component consisting of a steel plate connected using shear tabs to a reinforced concrete cover. The steel plate provides for stiffness, strength, and ductility and the concrete cover prevents the steel plate from buckling. In this paper, effects of steel plate's thickness, compressive strength and thickness of the concrete cover and spacing of the shear tabs on the characteristics of the wall in nonlinear lateral behaviour are evaluated and a macromodel substitute for the wall is developed. The macromodel is a generic lateral force-displacement rule for the wall with its characteristics as developed in this paper. Practical ranges of values are accounted for the parameters involved. Such an approach makes it possible to replace the very complicated and time-consuming three-dimensional model of the composite wall with a simple one-dimensional element following the nonlinear lateral force-displacement path as given in this paper.
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Poor seismic performance of older reinforced concrete buildings in past seismic events has frequently been attributed to failure of non-ductile columns not detailed for seismic demands. The Seismic Assessment of Existing Buildings Guidelines developed in New Zealand (NZ Guideline) provides a performance-based engineering framework for assessment of existing buildings, with concrete buildings covered in section C5. This study compares the probable failure mode and deformation capacity assessed based on NZ Guideline, ASCE/SEI 41-13, and ASCE/SEI 41-17 with the results from quasi-static cyclic tests conducted on 52 rectangular and 13 circular reinforced concrete columns with reinforcement details similar to those of non-ductile columns. Results indicate that the general curvature-based method of the NZ Guideline was not able to identify the observed failure mode but generally provides a conservative estimate of deformation capacity in comparison with ASCE/SEI 41-17. Based on the results of this study, a direct rotation-based acceptance criteria is proposed for NZ Guidelines. Also, slight modifications, to reduce conservatism, have been proposed for the curvature-based method.
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Seismic site amplification factors and seismic design spectra for bridges are influenced by site conditions that include geotechnical properties of soil strata as well as the geological setting. All modern seismic design codes recognize this fact and assign design spectral shapes based on site conditions or specify a 2-parameter model with site amplification factors as a function of site class, seismic intensity and vibration period (short and long). Design codes made a number of assumptions related to the site conditions while specifying the values of short (Fa) and long period (Fv) site amplification factors. Making these assumptions was necessary due to vast variation in site properties and limited availability of actual strong motion records on all site conditions and seismic setting in a region. This paper conducted a sensitivity analysis for site amplification factors for site classes C and D in the AASHTO bridge design code by performing a 1-D site response analysis in which values of site parameters like strata depth, travel-time averaged shear wave velocity in the top 30 m strata (Vs30), plasticity index (PI), impedance contrast ratio (ICR) and intensity of seismic ground motion were varied. The results were analyzed to identify the site parameters that impacted Fa and Fv values for site classes C and D. The computed Fa and Fv values were compared with the corresponding values in the AASHTO bridge design code and it was found that the code-based Fa and Fv values were generally underestimated and overestimated respectively.
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Small to Medium-sized Enterprises (SMEs) are often vulnerable to the adversities caused by major earthquake events, which may include business disruption, damage to goods and property, impaired employee health and safety, financial strain and loss of revenue, or even total loss of the business. SMEs are expected to make critical decisions to prepare their businesses for an earthquake, in an attempt to ensure business continuity and the wellbeing of their employees, should a disaster occur. This study was conducted five years after the devastating Canterbury earthquakes and sought to examine the level of earthquake preparedness of SMEs by investigating the actions undertaken in two different suburban locations having differing seismicity. The extent of preparedness was assessed based on a list of twenty-one possible actions grouped into four categories being knowledge enrichment, insurance and business continuity, survival support actions, and seismic damage mitigation. The assessment involved a survey with an online questionnaire. Analysis of the collected data revealed a specific adoption pattern in the regions of study. The main preparedness action adopted by SMEs was the purchase of business insurance with the development of continuity plans. The least obtained preparedness action was related to survival support actions such as maintaining necessary emergency supplies. The overall adoption rate of the preparedness actions was less than 30%, with no significant difference between the regions studied, and close to 50% of SMEs having adopted less than five preparedness actions. This situation clearly requires urgent attention from all stakeholders involved in SMEs resilience before an earthquake disaster hits the regions.
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Impulse ground motions are applied to single story structures with different in-plane wall strength and stiffness, rotational inertia, and out-of-plane wall stiffness to obtain the dynamic response considering torsion. A simple hand method to evaluate the impulse response is developed. It is shown that the median increase in response of the critical component considering torsion from many earthquake records is similar to that from impulse records. Using this information, a simple design methodology is proposed which enables the likely earthquake response of critical elements considering torsion to be obtained from building analyses not considering torsion. A design example is also provided.
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One method to rapidly estimate seismic losses during the structural design phase is to use contribution functions. These are relationships between expected losses (e.g. damage repair costs, downtime, and injury) for a wide range of building components (e.g. cladding, partitions, and ceilings) and the building’s response. This study aims to develop contribution functions for common types of cladding used in different types of buildings considering damage repair costs. In the first part of this study, a building survey was performed to identify types and quantity of cladding used in residential, commercial and industrial buildings in Christchurch, New Zealand; where it was found that the most common cladding types are glazing, masonry veneer, monolithic cladding and precast panels. The data collected during the survey was also used to develop cladding distribution (i.e. density) functions. The second step involved identifying fragility functions from relevant literature which are applicable to the cladding detailing used in New Zealand. The third step involved surveying consultants, suppliers and builders on typical repair/replacement cost. Finally, Monte Carlo simulations were performed to combine the cladding density function with the fragility functions and the repair cost for each type of cladding to derive contribution functions for various types of cladding and building usage. An example (case study) is provided to demonstrate its usage.
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Areas that experience permanent ground deformation in earthquakes (e.g., surface fault rupture, slope failure, and/or liquefaction) typically sustain greater damage and loss compared to areas that experience strong ground shaking alone. The 2016 Mw 7.8 Kaikōura earthquake generated ≥220 km of surface fault rupture. The amount and style of surface rupture deformation varied considerably, ranging from centimetre-scale distributed folding to metre-scale discrete rupture. About a dozen buildings – mainly residential (or residential-type) structures comprising single-storey timber-framed houses, barns and wool sheds with lightweight roofing material – were directly impacted by surface fault rupture with the severity of damage correlating with both local discrete fault displacement and local strain. However, none of these buildings collapsed. This included a house built directly atop a discrete rupture that experienced ~10 m of lateral offset. The foundation and flooring system of this structure allowed decoupling of much of the ground deformation from the superstructure thus preventing collapse. Nevertheless, buildings directly impacted by surface faulting suffered greater damage than comparable structures immediately outside the zone of surface rupture deformation. From a life-safety standpoint, all these buildings performed satisfactorily and provide insight into construction styles that could be employed to facilitate non-collapse performance resulting from surface fault rupture and, in certain instances, even post-event functionality.
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Seismic strengthening construction work has recently commenced on the Waikanae and Pakuratahi River Bridges assessed as having a high priority for retrofitting. Both bridges are on major State Highways in the Wellington region that carry high traffic volumes. The paper describes the assessment methods and strengthening details used on these two bridges.
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The past performance of foundations in earthquakes for timber dwellings prompted a practical investigation into the adequacy of existing sub-floor bracing, connection capacity and the overall adherence to NZS3604:1999. Using information gathered from a sample of 80 Wellington dwellings and by using the results from an Earthquake Loss modeller, it was found that the cost of upgrading “at risk” foundations is almost 30 times less expensive than the complete cost of rebuilding dwellings. Potential damage mitigation saves around 5 times the calculated total damage costs. This saving has the potential to reduce temporary shelter costs and other large unknown costs of post-earthquake rehabilitation and reconstruction.
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Structural engineers typically improve the seismic performance of deficient structures by adding strengthening elements to the structural system, which also add stiffness to the structure. However, as performance based design becomes more common practice, the focus is on the total performance of not only the structural system but the building components and contents. A stiffer and stronger building will generally be subjected to lower drifts but higher floor accelerations than a weaker and/or more flexible building. Reduced drift related damage may be accompanied by increased damage to components and contents which are sensitive to accelerations.
This paper examines two common forms of hardware used to strengthen existing buildings, buckling restrained braces (BRB) and viscous damping devices (VDD). Both types of device augment the existing structural system, rather than replace it. A series of nonlinear analyses is used to quantify the performance of two prototype frame buildings strengthened with each type of device. It is shown that equivalent structural performance, in terms of overall deformations, can be achieved with both types of device, and generally for lower cost by BRBs if only moderate levels of drift reduction are required. However, when the total building performance is examined the VDDs provide additional benefits in the form of reduced floor accelerations. The benefits of this may besufficient to warrant the higher cost solution.
